Analgesic nephropathy is an important public health problem in many Western societies. The use of analgesic and non-steroidal anti-inflammatory drugs (NSAIDs) is increasing. The ingestion of these agents, particularly NSAIDs, has been associated with significant morbidity and mortality. Renal Papillary Necrosis (RPN), the hallmark lesion of analgesic nephropathy, is a pathologic entity that is still poorly understood despite intensive research. The long-term goal of the proposed studies is to elucidate the pathologic mechanisms involved in RPN at the molecular level. We hypothesize that COX2 inhibitors (i.e. analgesics and NSAIDs) contribute to renal medullary cell death under hypertonic conditions through impairment of organic osmolyte accumulation. Our hypothesis is based on our exciting in vivo and in vitro data that show reduction of intracellular osmolyte concentrations in medullary kidney cells by COX2 inhibition and rescue of COX2 inhibitor-mediated apoptosis by osmolytes. Our hypothesis will be tested by examining the impact of COX2 inhibition on transcriptional regulation of osmolyte genes and osmolyte transporter activities in cultured mouse medullary interstitial cells (mMICs) under hypertonic conditions, as well as in mouse medullary kidney cells under dehydration in vivo (specific aim 1). We will then progress to investigate in the same model the induction mechanisms of apoptosis by COX2 inhibition and the antiapoptotic properties of organic osmolytes (specific aim 2). Finally, the role of cell signaling and nuclear signaling mechanisms involved in COX2- dependent survival mechanisms and regulation of osmolyte accumulation in mMICs will be defined (specific aim 3). RPN is a pathologic entity that is still poorly understood. The studies in this proposal address this major gap in our understanding of RPN. Our long-term goals are to gain insight into mechanistic processes that lead to this important health problem. It is necessary to understand these processes in order to design effective diagnostic procedures, therapeutic approaches and preventive measures for RPN.